1. Field of the Invention
This invention relates to a flexible tube for an endoscope and an electronic endoscope equipped with the flexible tube.
2. Description of the Prior Art
Generally, a flexible tube for an endoscope has a structure which includes a tubular core obtained by covering the outer periphery of a helical coil with a reticular tube (braided tube) and an outer cover formed of a synthetic resin or the like and provided over the outer periphery of the tubular core.
In endoscopic examination, the flexible tube for an endoscope is inserted along the body cavity to a deep part such as the stomach, duodenum, small intestine, and large intestine with being bent appropriately according to the shape of the path. In order to perform the inserting operation easily and reliably, it is necessary for the flexible tube that a push-in force applied to the proximal end (an end which is close to the operator) of the flexible tube is fully transmitted to its distal end. However, if bucking occurs in the flexible tube, the push-in force can not be fully transmitted to the distal end because the push-in force is partially absorbed by the bent part where the buckling occurs. This means that such a flexible tube for an endoscope can not achieve reliable inserting operation. In order to avoid the occurrence of such buckling, it is necessary for the flexible tube to have sufficient flexibility so that such buckling is hard to occur. Further, the outer cover must be firmly attached or bonded to the tubular core since buckling is liable to occur at areas where the outer cover is peeled off from the tubular core.
Furthermore, in order to perform the inserting operation easily and reliably, it is also necessary for the flexible tube that when a rotational force (a twist) is applied to the proximal end thereof, the rotation is fully transmitted to the distal end thereof without being absorbed somewhere along the flexible tube. In other word, a flexible tube for an endoscope is also required to have satisfactory rotation followability at the distal end thereof for rotational force applied at the proximal end.
One example of such flexible tubes is disclosed in Japanese Examined Patent Publication No. Hei 5-50287, in which an outer cover of a flexible tube for an endoscope is constructed from a double layer structure composed of an outer layer made of a material having good flexibility and an inner layer made of a material having good resilience, thereby improving resiliency of the flexible tube for an endoscope as a whole.
However, in the above-mentioned prior art, the adhesion (bonding strength) between the outer cover and the core has been left out of consideration. Therefore, in the flexible tube of the prior art, there is a case that the outer cover is peeled off from the core by repeated use thereof and thereby buckling is liable to occur and the resiliency of the flexible tube is lowered. In other words, the prior art flexible tube involves a problem in its durability.
It is therefore an object of the present invention to provide a flexible tube for an endoscope which has excellent resiliency and durability.
In order to achieve the above object, the present invention is directed to a flexible tube for an endoscope which comprises an elongated core body composed of a helical coil member which is formed by helically winding a flat band member and a braided member formed by braiding thin wires and provided over the coil; and a flexible outer cover for covering the core body. In the flexible tube, at least one of the thin wires has a coating layer and the flexible outer cover has a portion which is in contact with the coating layer of the thin wire of the braided member, in which the coating layer is formed of a material containing the material of the portion of the outer cover, and the material of the coating layer has a higher melting point than that of the material of the portion of the outer cover.
As described above, by forming such a coating layer on at least one of the fine wires, the present invention makes it possible to improve the adhesion between the braided member (reticular tube) and the outer cover. As a result, the present invention makes it possible to obtain a flexible tube for an endoscope having excellent resilience and durability. Further, it is also possible to prevent the coating layer from being melted when the outer cover is formed.
In a preferred embodiment, the coating layer contains a material that is the same as the material of the portion of the outer cover in the amount of 5 to 80 wt % thereof.
Further, in the preferred embodiment, the outer cover is formed of a material containing polyurethane based elastomer. This makes it possible to obtain a flexible tube for an endoscope having excellent flexibility.
Furthermore, in the preferred embodiment the coating layer is formed of a material containing polyurethane based elastomer. When such a material containing the polyurethane-based elastomer is employed as the constituent material of the coating layer 231, it is also possible to obtain excellent adhesion between the outer cover 3 and the coating layer 231 and it is also possible for the flexible tube 1 to have excellent flexibility in the case where the constituent material of the outer cover 3 is polyurethane-based elastomer (in particular, a material containing polyurethane-based elastomer as its main ingredient).
Moreover, in the preferred embodiment, the coating layer is formed of a material containing polyamide based elastomer. When the constituent material of the coating layer contains polyamide-based resin, it is possible to obtain excellent adhesion between the coating layer and the fine wires and excellent adhesion between the coating layer and the outer cover. This also improves the adhesion between the reticular tube and the outer cover, and as a result, the flexible tube will have excellent resilience and durability.
Moreover, in the preferred embodiment, the difference between the melting point of the material of the coating layer and the melting point of the material of the portion of the outer cover is in the range of 4 to 200xc2x0 C.
In the present invention, it is preferred that the average thickness of the coating layer is in the range of 0.01 to 0.1 mm.
Further, it is also preferred that the average thickness of the outer cover is in the range of 0.01 to 1.5 mm.
Furthermore, it is also preferred that the outer cover is formed by extrusion molding.
In another preferred embodiment of the present invention, the outer cover is formed into a laminated structure including an inner layer, an intermediate layer and an outer layer, and the inner layer is formed of a material that exhibits adhesion with the coated layer. This makes it possible to provide a narrow flexible tube for an endoscope.
Another aspect of the present invention is directed to an electronic endoscope, comprising an operation section which is operated by an operator; and a flexible tube having a proximal end connected to the operation section at the proximal end thereof, the flexible tube including an elongated tubular core composed of a helical tubular member which is formed by helically winding a flat band member and a braided member formed by braiding thin wires and an a flexible outer cover formed of a synthetic resin and provided over the outer periphery of the tubular core, wherein at least one of the thin wires has a coating layer and the flexible outer cover has a portion which is in contact with the coating layer of the thin wire of the braided member, in which the coating layer is formed of a material containing the material of the portion of the outer cover and the material of the coating layer has a higher melting point than that of the material of the portion of the outer cover.
Further, in a preferred embodiment, the outer cover is formed into a laminated structure including an inner layer, an intermediate layer and an outer layer, and the inner layer is formed of a material that exhibits adhesion with the coated layer. This makes it possible to provide an arrow flexible tube for an endoscope.
These and other objects, structures and results of the present invention will be apparent more clearly when the following detailed description of the preferred embodiments is considered taken in conjunction with the accompanying drawings.